Atomising nozzles are used in a wide range of spray devices to break up a fluid into fine droplets so as to form a spray or mist of the fluid as it is discharged from the device. Where a medicament is to be administered deep into the lung of a user, the droplet size in such a spray should be less than 10 micrometers.
Currently, the accepted method for dispensing a fluid medicament uses a pressurised or liquefied propellant gas as the means for atomising the fluid medicament composition. The rapid expansion of the propellant at the nozzle orifice causes the atomization of the fluid into droplets of a sufficiently small size for administration of medicaments via the lungs. At present, the use of such propellant systems provides the only practical means for administering medicaments by this route using convenient hand portable devices. However, the use of such gases has a number of disadvantages, for example from environmental aspects or from the chilling sensations experienced by the user due to the rapid evaporation of the propellant from the composition, and the fact that many medicament formulations are incompatible with conventionally used propellants without the use of co-solvents and other additives, which may themselves be undesirable.
Many attempts have been made to avoid the use of such pressurised gases as propellants in medicament formulations, for example using mechanical means to atomise the fluid. Most such attempts have failed because they cannot achieve the very small droplet size required within a hand held device.
In order to assist break up of a stream or jet of fluid issuing from a nozzle orifice, it has been proposed that the stream or jet of fluid should strike an impingement surface placed some distance from the outlet of the nozzle assembly. Such devices may produce sprays in which some of the droplets have a small diameter, but many of the droplets will be of excessively large size for inhalation deep into the lung of a user, thus affecting the uptake of the medicament by the user. Furthermore, some of the fluid striking the impingement surface adheres to the surface. As a result, a fluctuating amount of any measured dose of the fluid is lost. In addition, the residual fluid adhering to the impingement surface can become contaminated and must be removed before the next dose of fluid strikes the surface. Such impingement mechanisms cannot therefore be used where a consistent and predetermined quantity of fluid is to be dispensed to a user, notably where the fluid contains a medicament which is to be inhaled deep into the lungs of a user.
It has also been proposed to pass the fluid through a swirl chamber located upstream of the inlet to the nozzle assembly. Such a swirl chamber imparts rotation to the fluid stream and causes the fluid to issue from the nozzle orifice as a swirling cone of fluid which readily breaks up into a spray of fine droplets. However, due to difficulties in manufacture, it has not proved commercially feasible to manufacture such a swirl chamber for small scale devices, for example those where a fluid is ejected under pressure without the aid of a pressurised gas stream through a very fine nozzle orifice. The use of a swirl chamber has therefore not provided a practical solution with small scale devices.
The present application relates to a configuration of nozzle assembly, notably of the nozzle orifice aperture itself, which assists production of a finely atomised spray by the creation of secondary flows, that is flows of fluid transverse to the main line of flow of fluid, at or adjacent the aperture to the nozzle orifice by inducing changes in the direction of flow of the fluid as it passes through the nozzle bore or aperture. Such nozzle assemblies enhance the production of very fine droplets in the spray, notably those with a mass median particle size less than 10 micrometers, and enhance the operation of mechanically operated devices for the production of atomised sprays to be inhaled deep into the lung of a user.